FIG. 16 is a diagram showing one example of a light-emitting device. The light-emitting device of this example includes at least one light-emitting element (in FIG. 16, light-emitting diodes) Z1, a light-emitting element driver IC (integrated circuit) 100 which drives the light-emitting element Z1, a P-channel MOS (metal-oxide-semiconductor) transistor P1 which is inserted in the power feed path from the light-emitting element driver IC 100 to the light-emitting element Z1, a controller IC 200 which feeds the light-emitting element driver IC 100 with a PWM (pulse-width modulation) dimming signal S1, and a monitor IC 300 which checks for a fault in the controller IC 200.
The light-emitting element driver IC 100 is a semiconductor integrated circuit device that has integrated into it an output voltage generator 101, which generates a constant output voltage Vo from an input voltage Vi to feed the output voltage Vo to the light-emitting element Z1, and an output current controller 102, which turns the transistor P1 ON and OFF according to the PWM dimming signal S1 output from the controller IC 200 to control the duty of an output current Io through the light-emitting element Z1 (thereby to control the luminance of the light-emitting element Z1). To increase the luminance of the light-emitting element Z1, the ON duty of the PWM dimming signal S1 (the proportion of the ON period Ton in the period T shown in FIG. 17) is set at a larger value; reversely, to decrease the luminance of the light-emitting element Z1, the ON duty of the PWM dimming signal S1 is set at a smaller value. The light-emitting element driver IC 100 also has external terminals T11 to T14. To the external terminal T11, the input voltage Vi is applied. From the external terminal T12, the output voltage Vo is output. To the external terminal T13, the PWM dimming signal S1 is fed. From the external terminal T14, a gate control signal for turning the transistor P1 ON and OFF is output.
The controller IC 200 is a semiconductor integrated circuit device that has integrated into it a clock circuit 201, which generates a clock signal S2, and a PWM circuit 202, which generates the PWM dimming signal S1 based on the clock signal S2. The controller IC 200 also has external terminals T21 to T23. From the external terminal T21, the PWM dimming signal S1 is output. From the external terminal T22, the clock signal S2 is output. To the external terminal T23, the monitoring result signal S3 is fed. There is no particular restriction on how the controller IC 200 uses the monitoring result signal S3; for example, in one conceivable configuration, when the monitoring result signal S3 is in a state that indicates a fault in the controller IC 200, the operation of the controller IC 200 can be stopped completely for increased safety.
The monitor IC 300 has external terminals T31 and T32. Based on the clock signal S2 fed to the external terminal T31, the monitor IC 300 checks whether or not the controller IC 200 is faulty to output the check result, as the monitoring result signal S3, from the external terminal T32. In this example, when the controller IC 200 is not faulty, the monitoring result signal S3 is at HIGH level, and when the controller IC 200 is faulty, the monitoring result signal S3 is at LOW level. That is, a LOW-level monitoring result signal S3 serves as a signal that indicates a fault in the controller IC 200.
Although in FIG. 16 the monitoring result signal S3 is fed only to the controller IC 200, this is not meant as any limitation; for example, instead of the controller IC 200, or in addition to the controller IC 200, a controller that controls the entire appliance that incorporates the light-emitting device shown in FIG. 16 may be fed with the monitoring result signal S3. Although in FIG. 16 the monitor IC 300 checks for only a fault in the controller IC 200, a configuration is also possible where the controller IC 200 and the monitor IC 300 each check for a fault in the other.